EG2008

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https://diglib.eg.org/handle/10.2312/264

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Modeling a Generic Tone-mapping Operator
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Mantiuk, Rafal; Seidel, Hans-Peter
Although several new tone-mapping operators are proposed each year, there is no reliable method to validate their performance or to tell how different they are from one another. In order to analyze and understand the behavior of tone-mapping operators, we model their mechanisms by fitting a generic operator to an HDR image and its tone-mapped LDR rendering. We demonstrate that the majority of both global and local tone-mapping operators can be well approximated by computationally inexpensive image processing operations, such as a per-pixel tone curve, a modulation transfer function and color saturation adjustment. The results produced by such a generic tone-mapping algorithm are often visually indistinguishable from much more expensive algorithms, such as the bilateral filter. We show the usefulness of our generic tone-mapper in backward-compatible HDR image compression, the black-box analysis of existing tone mapping algorithms and the synthesis of new algorithms that are combination of existing operators.
The Shadow Meets the Mask: Pyramid-Based Shadow Removal
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Shor, Yael; Lischinski, Dani
In this paper we propose a novel method for detecting and removing shadows from a single image thereby obtaining a high-quality shadow-free image. With minimal user assistance, we first identify shadowed and lit areas on the same surface in the scene using an illumination-invariant distance measure. These areas are used to estimate the parameters of an affine shadow formation model. A novel pyramid-based restoration process is then applied to produce a shadow-free image, while avoiding loss of texture contrast and introduction of noise. Unlike previous approaches, we account for varying shadow intensity inside the shadowed region by processing it from the interior towards the boundaries. Finally, to ensure a seamless transition between the original and the recovered regions we apply image inpainting along a thin border. We demonstrate that our approach produces results that are in most cases superior in quality to those of previous shadow removal methods. We also show that it is possible to easily composite the extracted shadow onto a new background or modify its size and direction in the original image.
Computer Graphics Curriculum: a Programming Approach
(The Eurographics Association, 2008) Sobczyk, Dominique; Touzeau, Marie-Solange; Bourdin, Jean-Jacques; Steve Cunningham and Lars Kjelldahl
At University Paris 8 the computer science curriculum is focused on programming as a good technique to improve the skills of students and to improve the success of studies. It has been reinforced when France adopted the Bologna requirements. This approach is well adapted to our computer graphics courses. The results of these courses are discussed.
Ray Casting Algebraic Surfaces using the Frustum Form
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Reimers, Martin; Seland, Johan
We propose an algorithm for interactive ray-casting of algebraic surfaces of high degree. A key point of our approach is a polynomial form adapted to the view frustum. This so called frustum form yields simple expressions for the Bernstein form of the ray equations, which can be computed efficiently using matrix products and pre-computed quantities. Numerical root-finding is performed using B-spline and Bezier techniques, and we compare the performances of recent and classical algorithms. Furthermore, we propose a simple and fairly efficient anti-aliasing scheme, based on a combination of screen space and object space techniques. We show how our algorithms can be implemented on streaming architectures with single precision, and demonstrate interactive frame-rates for degrees up to 16.
Image-based Aging Using Evolutionary Computing
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Hubball, Daniel; Chen, Min; Grant, Phil W.
Aging has considerable visual effects on the human face and is difficult to simulate using a universally-applicable global model. In this paper, we focus on the hypothesis that the patterns of age progression (and regression) are related to the face concerned, as the latter implicitly captures the characteristics of gender, ethnic origin, and age group, as well as possibly the person-specific development patterns of the individual. We use a data-driven framework for automatic image-based facial transformation in conjunction with a database of facial images. We build a novel parameterized model for encoding age-transformation in addition with the traditional model for face description. We utilize evolutionary computing to learn the relationship between the two models. To support this work, we also developed a new image warping algorithm based on non-uniform radial basis functions (NURBFs). Evolutionary computing was also used to handle the large parameter space associated with NURBFs. In comparison with several different methods, it consistently provides the best results against the ground truth.
Deep Opacity Maps
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Yuksel, Cem; Keyser, John
We present a new method for rapidly computing shadows from semi-transparent objects like hair. Our deep opacity maps method extends the concept of opacity shadow maps by using a depth map to obtain a per pixel distribution of opacity layers. This approach eliminates the layering artifacts of opacity shadow maps and requires far fewer layers to achieve high quality shadow computation. Furthermore, it is faster than the density clustering technique, and produces less noise with comparable shadow quality. We provide qualitative comparisons to these previous methods and give performance results. Our algorithm is easy to implement, faster, and more memory efficient, enabling us to generate high quality hair shadows in real-time using graphics hardware on a standard PC.
eNVyMyCar: a Multi-player Car Racing Game for Teaching Computer Graphics
(The Eurographics Association, 2008) Ganovelli, Fabio; Corsini, Massimiliano; Steve Cunningham and Lars Kjelldahl
The development of a computer game is widely used as a means to convey Computer Sciences concepts. There are several reasons for that: it stimulates creativity, it provides an immediate sense of achievement when the code works, it typically covers all the aspects of an introductory course, it is easy to find ideas just looking around. In this paper we present NVMC (eNVy My Car), a framework for collaborative/competitive development of a computer game, and report the experience in using it in two Computer Graphics courses held in the year 2007 by the authors. We developed a multiplayer car racing game where the student is only asked to implement the rendering of the scene, while all the other aspects, communication and synchronization are implemented in the framework and transparent to the developer. The novelty of our framework is that all the clients on-line are able to see the views provided by the other clients, which serves to motivate the students to improve their work by comparing it with the other clients, as a means to pick up ideas from the others and finally to show off with their classmates.
Video Relighting Using Infrared Illumination
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Wang, Oliver; Davis, James; Chuang, Erika; Rickard, Ian; De Mesa, Krystle; Dave, Chirag
Inappropriate lighting is often responsible for poor quality video. In most offices and homes, lighting is not designed for video conferencing. This can result in unevenly lit faces, distracting shadows, and unnatural colors. We present a method for relighting faces that reduces the effects of uneven lighting and color. Our setup consists of a compact lighting rig and a camera that is both inexpensive and inconspicuous to the user. We use unperceivable infrared (IR) lights to obtain an illumination bases of the scene. Our algorithm computes an optimally weighted combination of IR bases to minimize lighting inconsistencies in foreground areas and reduce the effects of colored monitor light. However, IR relighting alone results in images with an unnatural ghostly appearance, thus a retargeting technique is presented which removes the unnatural IR effects and produces videos that have substantially more balanced intensity and color than the original video.
CHC++: Coherent Hierarchical Culling Revisited
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Mattausch, Oliver; Bittner, Jiri; Wimmer, Michael
We present a new algorithm for efficient occlusion culling using hardware occlusion queries. The algorithm significantly improves on previous techniques by making better use of temporal and spatial coherence of visibility. This is achieved by using adaptive visibility prediction and query batching. As a result of the new optimizations the number of issued occlusion queries and the number of rendering state changes are significantly reduced. We also propose a simple method for determining tighter bounding volumes for occlusion queries and a method which further reduces the pipeline stalls. The proposed method provides up to an order of magnitude speedup over the previous state of the art. The new technique is simple to implement, does not rely on hardware calibration and integrates well with modern game engines.
Removing Artifacts Due To Frequency-Domain Processing of Light-Fields
(The Eurographics Association, 2008) Intwala, Chintan; Georgeiv, Todor; Katerina Mania and Eric Reinhard
In previous works, light-field capture has been analyzed in spatio-angular representation. A light-field camera samples the optical signal within a single photograph by multiplexing the 4D radiance onto the physical 2D surface of the sensor. Besides sampling the light field spatially, methods have been developed for multiplexing the radiance in the frequency domain by optically mixing different spatial and angular frequency components. The mathematical method for recovering the multiplexed spatial and angular information from the frequency representation is very straightforward. However, the results are prone to lots of artifacts due to limitations inherent to frequency-domain processing of images. In this paper, we try understand the characteristics of these artifacts. Furthermore, we study the effect and sources of artifacts that affect the quality of the results and present various methods for the removal of artifacts.
Measuring and Enhancing the Legibility of GPU-rendered Text
(The Eurographics Association, 2008) Tycowicz, Christoph von; Loviscach, Joern; Katerina Mania and Eric Reinhard
Whereas the rendering of tiny typefaces in 2D applications has been perfected over decades, the legibility of text in 3D visualizations has rarely been addressed. This affects road signs, meters, screens, and books in virtual reality applications ranging from car driving simulators to digital lecture halls. To improve text rendering and display, we devised a lightweight psychovisual test to measure one prominent aspect of legibility. We subjected promising GPU-based methods for crisp minification to this test. It turned out that legibility may be improved without undue costs. Not all techniques whose results look appealing on first sight will, however, enhance legibility.
Floating Textures
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Eisemann, M.; De Decker, B.; Magnor, M.; Bekaert, P.; De Aguiar, E.; Ahmed, N.; Theobalt, C.; Sellent, A.
We present a novel multi-view, projective texture mapping technique. While previous multi-view texturing approaches lead to blurring and ghosting artefacts if 3D geometry and/or camera calibration are imprecise, we propose a texturing algorithm that warps ( floats ) projected textures during run-time to preserve crisp, detailed texture appearance. Our GPU implementation achieves interactive to real-time frame rates. The method is very generally applicable and can be used in combination with many image-based rendering methods or projective texturing applications. By using Floating Textures in conjunction with, e.g., visual hull rendering, light field rendering, or free-viewpoint video, improved rendering results are obtained from fewer input images, less accurately calibrated cameras, and coarser 3D geometry proxies.
Agile Spectrum Imaging: Programmable Wavelength Modulation for Cameras and Projectors
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Mohan, Ankit; Raskar, Ramesh; Tumblin, Jack
We advocate the use of quickly-adjustable, computer-controlled color spectra in photography, lighting and displays. We present an optical relay system that allows mechanical or electronic color spectrum control and use it to modify a conventional camera and projector. We use a diffraction grating to disperse the rays into different colors, and introduce a mask (or LCD/DMD) in the optical path to modulate the spectrum. We analyze the trade-offs and limitations of this design, and demonstrate its use in a camera, projector and light source. We propose applications such as adaptive color primaries, metamer detection, scene contrast enhancement, photographing fluorescent objects, and high dynamic range photography using spectrum modulation.
Perceptually-Motivated Graphics
(The Eurographics Association, 2008) Mania, Katerina; Reinhard, Erik; Maria Roussou and Jason Leigh
In this half-day tutorial, we give an overview of the uses of knowledge about the human visual system, as applied to several aspects of computer graphics. In particular, we show how human visual perception applies to the optimization of rendering algorithms, display algorithms, as well as virtual environments. Examples are shown for applications such as real-time rendering, high quality rendering, material editing using images, and training and knowledge transfer in virtual environments. The aim is to show that the human visual perception literature harbours a rich source of knowledge that can be directly applied to improve a wide range of algorithms and technologies in computer graphics.
Crowds in Context: Evaluating the Perceptual Plausibility of Pedestrian Orientations
(The Eurographics Association, 2008) Peters, Christopher; Ennis, Cathy; McDonnell, Rachel; O'Sullivan, Carol; Katerina Mania and Eric Reinhard
We describe a work-in-progress evaluating the plausibility of pedestrian orientations. While many studies have focused on creating accurate or fast crowd simulation models for populating virtual cities or other environments, little is known about how humans perceive the characteristics of generated scenes. Our initial study, reported here, consists of an evaluation based on static imagery reconstructed from annotated photographs, where the orientations of individuals have been modified. An important focus in our research is the consideration of the effects of the context of the scene on the evaluation, in terms of nearby individuals, objects and the constraints of the walking zone. This work could prove significant for improving and informing the creation of computer graphics pedestrian models. Our particular aim is to inform level-of-detail models
Graphics based Computer Adaptive Testing and Beyond
(The Eurographics Association, 2008) Cheng, Irene; Basu, Anup; Steve Cunningham and Lars Kjelldahl
Instead of computer games, animations, cartoons, and videos being used only for entertainment by kids, there is now an interest in using graphics for 'innovative testing'. Rather than traditional pen-and-paper tests, audio, video and graphics are being conceived as alternative means for more effective testing in the future. In this paper we review some examples of graphics item types for testing. As well, we outline how games can be used to interactively test concepts; discuss designing chemistry item types with interactive graphics; suggest approaches for automatically adjusting difficulty level in interactive graphics based questions; and propose strategies for giving partial marks for incorrect answers. We study how to test different cognitive skills, such as music, using multimedia interfaces; and also evaluate the effectiveness of our model. A method for estimating difficulty level of a mathematical item type using Item Response Theory (IRT) is discussed. Evaluation of the graphics item types through extensive testing on some students is also described. All of the graphics implementations shown in this report are developed by members of our research group.
Adaptive Remeshing of Non-Manifold Surfaces
(The Eurographics Association, 2008) Zilske, Michael; Lamecker, Hans; Zachow, Stefan; Katerina Mania and Eric Reinhard
We present a unified approach for consistent remeshing of arbitrary non-manifold triangle meshes with additional user-defined feature lines, which together form a feature skeleton. Our method is based on local operations only and produces meshes of high regularity and triangle quality while preserving the geometry as well as topology of the feature skeleton and the input mesh.
Interactive Volume Rendering with Dynamic Ambient Occlusion and Color Bleeding
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Ropinski, Timo; Meyer-Spradow, Jennis; Diepenbrock, Stefan; Mensmann, Joerg; Hinrichs, Klaus
We propose a method for rendering volumetric data sets at interactive frame rates while supporting dynamic ambient occlusion as well as an approximation to color bleeding. In contrast to ambient occlusion approaches for polygonal data, techniques for volumetric data sets have to face additional challenges, since by changing rendering parameters, such as the transfer function or the thresholding, the structure of the data set and thus the light interactions may vary drastically. Therefore, during a preprocessing step which is independent of the rendering parameters we capture light interactions for all combinations of structures extractable from a volumetric data set. In order to compute the light interactions between the different structures, we combine this preprocessed information during rendering based on the rendering parameters defined interactively by the user. Thus our method supports interactive exploration of a volumetric data set but still gives the user control over the most important rendering parameters. For instance, if the user alters the transfer function to extract different structures from a volumetric data set the light interactions between the extracted structures are captured in the rendering while still allowing interactive frame rates. Compared to known local illumination models for volume rendering our method does not introduce any substantial rendering overhead and can be integrated easily into existing volume rendering applications. In this paper we will explain our approach, discuss the implications for interactive volume rendering and present the achieved results.
GPU Accelerated Direct Volume Rendering on an Interactive Light Field Display
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Agus, Marco; Gobbetti, Enrico; Guitian, Jose Antonio Iglesias; Marton, Fabio; Pintore, Giovanni
We present a GPU accelerated volume ray casting system interactively driving a multi-user light field display. The display, driven by a single programmable GPU, is based on a specially arranged array of projectors and a holographic screen and provides full horizontal parallax. The characteristics of the display are exploited to develop a specialized volume rendering technique able to provide multiple freely moving naked-eye viewers the illusion of seeing and manipulating virtual volumetric objects floating in the display workspace. In our approach, a GPU ray-caster follows rays generated by a multiple-center-of-projection technique while sampling pre-filtered versions of the dataset at resolutions that match the varying spatial accuracy of the display. The method achieves interactive performance and provides rapid visual understanding of complex volumetric data sets even when using depth oblivious compositing techniques.
Reduced Depth and Visual Hulls of Complex 3D Scenes
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Bogomjakov, Alexander; Gotsman, Craig
Depth and visual hulls are useful for quick reconstruction and rendering of a 3D object based on a number of reference views. However, for many scenes, especially multi-object, these hulls may contain significant artifacts known as phantom geometry. In depth hulls the phantom geometry appears behind the scene objects in regions occluded from all the reference views. In visual hulls the phantom geometry may also appear in front of the objects because there is not enough information to unambiguously imply the object positions.In this work we identify which parts of the depth and visual hull might constitute phantom geometry. We define the notion of reduced depth hull and reduced visual hull as the parts of the corresponding hull that are phantom-free. We analyze the role of the depth information in identification of the phantom geometry. Based on this, we provide an algorithm for rendering the reduced depth hull at interactive frame-rates and suggest an approach for rendering the reduced visual hull. The rendering algorithms take advantage of modern GPU programming techniques.Our techniques bypass explicit reconstruction of the hulls, rendering the reduced depth or visual hull directly from the reference views.

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